Networking and Kubernetes

Chapter 2. Linux Networking

To understand the implementation of networking in Kubernetes, we will need to understand the fundamentals of networking in Linux. Ultimately, Kubernetes is a complex management tool for Linux (or Windows!) machines, and this is hard to ignore while working with the Kubernetes network stack. This chapter will provide an overview of the Linux networking stack, with a focus on areas of note in Kubernetes. If you are highly familiar with Linux networking and network management, you may want to skim or skip this chapter.

Tip

This chapter introduces many Linux programs. Manual, or man, pages, accessible with man <program>, will provide more detail.

Basics

Let’s revisit our Go web server, which we used in Chapter 1. This web server listens on port 8080 and returns “Hello” for HTTP requests to / (see Example 2-1).

Example 2-1. Minimal web server in Go

package main

import (
	"fmt"
	"net/http"
)

func hello(w http.ResponseWriter, _ *http.Request) {
	fmt.Fprintf(w, "Hello")
}

func main() {
	http.HandleFunc("/", hello)
	http.ListenAndServe("0.0.0.0:8080", nil)
}

Warning

Ports 1–1023 (also known as well-known ports) require root permission to bind to.

Programs should always be given the least permissions necessary to function, which means that a typical web service should not be run as the root user. Because of this, many programs will listen on port 1024 or higher (in particular, port 8080 is a common choice for HTTP services). When possible, listen on a nonprivileged ...